Under reasonable conditions of temperature below about 100.degree. C. and pressures of about 2 atmospheres or less, gas phase etch of silicon oxide using anhydrous HF is generally impractical without a second chemical which participates in some way to allow the etch reaction to proceed at a practical rate. A variety of chemicals which facilitate silicon oxide removal with HF are known in the art, including water, alcohols, ketones and some carboxylic acids. Such compounds are liquids at ambient pressure and temperature. Similarly, U.S. Pat. Nos. 5,094,701, 5,221,366, 5,213,621, 5,213,622, and 5,332,444 describe techniques for gas phase removal of metals, metal nitrides or metal oxides which employ HF and a second chemical, such as a beta-diketone, beta-ketoimide, halogenated carboxylic acid or hexamethyl disilazane which functions as a complexing reagent to produce volatile metal-ligand complexes which then can be sublimed from the surface.
It has long been known that gas phase HF/water mixtures can be used to etch various silicon oxide films. Early references include J. P. Holmes, et al, "A Vapor Etching Technique for the Photolithography of Silicon Dioxide," Microelectronics and Reliability, 5 pp 337-341 (1966); and K. Beyer, et al, "Etching of SiO.sub.2 in Gaseous HF/H.sub.2 O," IBM Technical Bulletin, 19(7) (December 1976), both of which used a HF/water azeotrope.
In U.S. Pat. No. 4,749,440 (Blackwood), a process for removing silicon oxide films from silicon wafers using anhydrous HF gas and water vapor carried in a nitrogen stream is disclosed. The use of anhydrous HF provides improved process control. An ambient pressure apparatus for performing this process is currently commercially available from FSI International, Inc., under the trademark Excalibur.RTM..
Various publications describe gas-phase HF/alcohol processes for etching silicon oxide.
U.S. Pat. No. 5,022,961, (Izumi), describes a process for removing a film of a silicon oxide, from a silicon substrate. Two steps are identified:
(a) placing the substrate in a reaction chamber to be isolated in an air-tight manner from the outside air, and PA1 (b) feeding anhydrous hydrogen fluoride and alcohol simultaneously into the reaction chamber. PA1 a) exposing the surface in a process chamber to a gaseous reactant mixture comprising: PA1 b) removing volatile products from the process chamber, wherein PA1 the gaseous reactant mixture further comprises
The reference indicates that the HF/alcohol feeds may be as liquid solutions or gas mixtures. A similar disclosure of an ambient pressure gas phase etch process is contained in A. Izumi, et al, "A New Cleaning Method by Using Anhydrous HF/CH.sub.3 OH Vapor System," J. Ruzyllo et al, ed., Symposium on Cleaning Technology in Semiconductor Device Manufacturing, ECS Proceedings, 92(12), pp 260-266 (1992).
WO 94/27315 discloses gas phase etching of oxide layers with hydrogen fluoride and one or more carboxylic acids.
U.S. Pat. No. 5,439,553 (Grant, et al), issued Aug. 8, 1995 from an application filed in the United States on Mar. 30, 1994, describes and claims a low pressure process for removing silicon oxide from a wafer substrate in which an HF/alcohol gas mixture is used at a low pressure.
J. Butterbaugh, et al, "Gas Phase Etching of Silicon Oxide with Anhydrous HF and Isopropanol," Proceedings of the Third International Symposium on Cleaning Technology in Semiconductor Device Manufacturing, ECS Proceedings, 94(7) pp 374-383 (1994), describe a low pressure HF/isopropanol etch process for silicon oxide.
Low pressure processes generally are of increasing interest as cluster tools come into use in the semiconductor manufacturing industry. Cluster tools link a series of separate process modules via a central robotic handler, operating at a pressure of about 100 torr or less, allowing substrates such as silicon wafers to undergo multiple sequential processes without exposure to the environment. Such environmental isolation is becoming increasingly important as device features shrink, causing smaller and smaller contaminant regions to become problematic, and ultralarge scale integration increases the investment represented in each defective chip.
WO 97/15069 is directed to a process for removing Group 4-13 metallic material from a substrate using a reactive halogen component and also an activated halosilane component.
Copending U.S. application Ser. No. 08/824,512 filed Mar. 26, 1997, the contents of which are hereby incorporated by reference, discloses an apparatus and method for direct delivery of enabling chemical gas from a liquid source and of HF gas in a hydrogen fluoride/enabling chemical based cleaning or etching process, such as a silicon dioxide film etching process. As used therein the term "enabling chemical" refers to second chemicals which participate in the cleaning or etching process as a catalyst, co-reactant, and/or complexing agent.